SCH4C                       Lab #21 - Electroplating
Introduction:  When two dissimilar metals are placed together in an electrolyte and connected by means of a conducting wire, electric current is generated.  This is the basis of an electrochemical cell.  Conversely, when an electrochemical cell is operated in the reverse manner by applying an external power supply over-voltage, the same cell reaction will create an electrolytic cell.  In this case the metals, are "plated" out on the cathode.  This is the principle used in industry for electroplating.  The object to be plated is made the cathode, while the anode is made of the metal used for plating.  For good deposition on it, the cathode must be free of grease, and the correct plating solution and current density must also be carefully considered.  In this experiment, you will explore some simple means of plating one metal onto another.
Problem:   How does the operation of an electrolytic cell create to potential to electroplate out Cu, zinc , or silver.
Apparatus:   DC power supply, beakers, electrode support, sandpaper or steel wool, connecting wires
Materials:   Strips of metals, copper, zinc and silver, zinc plating solution, 1.0 M zinc sulphate, 6.0 M NaOH solution, acetone, conc. NH3 solution.  distilled water, copper plating solution, copper(II) sulphate, sulphuric acid, silver plating solution, silver nitrate, sodium hydroxide and concentrated ammonia.
Safety:   Silver nitrate solution can stain hands and clothing permanently.  DO NOT spill.  Copper and zinc plating solution are poisonous.  They must be disposed of properly according to the local WHMIS standards for hazardous materials.  Sodium hydroxide and sulphuric acid are corrosive.  Avoid any spills.  Concentrated ammonia is very irritating to the eyes.  Acetone is poisonous and flammable.  Do not use it near sparks or flames.  Beware of possible electrical shock in this experiment.  Return ALL plating solutions to your teacher for proper disposal.
Procedure:
Part I:
1.  Obtain about 200 mL of the zinc plating solution in a clean, dry 250 mL beaker.
2. Clean the copper electrode (or a brass object or a copper coin) with sandpaper or steel wool.  Rinse with distilled water and then with acetone.  DO NOT TOUCH this with your fingers.  Handle by the edges only.  This  object will serve as the cathodic electrode.
3. Suspend the copper cathode and a zinc electrode (a anode) in the beaker of plating solution by means of an electrode holder.
4. Connect the electrode so that the negative power supply is attached to the copper electrode.  Adjust the power supply to give a current flow of about 0.50 amps and allow the electrolysis to proceed for about 20 minutes.
5. Disconnect the power supply.  Remove the copper cathode, wash with distilled water and then with acetone.  Record the changes observed in the colour and appearance of the electrode.  Dispose of the plating solution according to your teacher's instructions.

Part II
6. Obtain about 200 mL of copper plating solution in a 250 mL beaker
7. Repeat Procedures 2 to 5, using a copper strip for the anode.

Part III
8. Obtain about 200 mL of silver plating solution in a clean 250 mL beaker
9. Repeat Procedures 2 to 5, using a copper strip for the anode.
Concluding Questions
1. Explain why some of the plating does not seem to adhere well to the object.
2. List some of the possible sources of error.
3. Explain why silver nitrate is not used directly for the electrolysis.
4. Write the balanced equations for the reactions involved in the preparation of the silver plating solution.
5, List all the cell reactions in the experiment.
6. Use the Internet or library to find out how an object is plated industrially with
a) chromium      b) gold